1. Field of the Invention
This invention relates to use of molecular sieves in pressure swing adsorption and vacuum swing adsorption processes for dehydrating feedstocks of alcohols and other gases or vapors, and further relates to methods and apparatus for periodically regenerating the molecular sieves for continuing successful practice of the dehydrating processes.
As used herein, the term “vapor” refers to a gas that is easily condensable at normal operating temperatures and pressures, whereas the term “gas” refers to the gaseous phase material that is not readily or ordinarily condensable at conventional operating temperatures and pressures. More specifically, the term “vapors” refers to materials that are condensable to liquid at temperatures from −50° F. to 300° F., and at pressures from as low as 1 mm. absolute to as high as 100 psi gauge.
2. Description of the Prior Art
Presumably relevant patent prior art includes United States published patent applications US 2009/0301970; US 2009/0107331; US 2008/0202337; US 2008/0207959; US 2008/0209892; and US 2008/0148718; U.S. Pat. Nos. 6,605,136; 6,506,234; 6,098,425; 5,985,003; 5,917,078; 5,503,658; 5,335,426; 4,971,606; 4,964,888; 4,948,391; 4,926,643; 4,726,818; 4,696,720; 4,687,498; 4,556,460; 4,487,614; 4,273,621; and 4,093,429; as well as published PCT applications WO 2008/089527; WO 2008/079858; and WO 2005/118126.
Presumably relevant printed non-patent prior art includes the publications Shipboard Gas Generation Using Molecular Sieves, Ortmann, LCdr. Robert A., USN, Woerner, Joseph A., Navel Engineers Journal, Volume 97, Issue 1, p. 58-63, Published Online: 18 Mar. 2009; Air Separation Control Technology, Vinson, David R., Computers & Chemical Engineering, Volume 30, Issues 10-12, September 2006, pp. 1436-1446; Molecular Sieves as Catalysts for Methanol Dehydration in the LPDME™ Process, Wang, Andrew W., Weigel, Scott and Muraro, Giovanni, Air Products and Chemicals, Inc., DE-FC22-95PC93052, April 2002; The Effects of a Readily Adsorbed Trace Component (Water) in a Bulk Separation PSA Process: The Case of Oxygen VSA, Wilson, Simon J., Beh, Chris C. K., Webley, Paul A., and Todd, Richard S., Ind. Eng. Chem. Res., 2001, 40 (12), pp. 2702-2713; Sour Gas Dehydration Technology and Alternatives, Blachman, Marc, Presented at the LRGC, Feb. 27-Mar. 1, 2000, Norman, Oklahoma; Pressure Swing Adsorption for Air Purification. 1. Temperature Cycling and Role of Weekly Adsorbed Carrier Gas, Friday, David K., Ind. Eng. Chem. Res., 1996, 35 (7), pp. 2342-2354; Air Separation by Pressure Swing Adsorption, Ruthven, D. M. and Farooq, S., Gas Separation & Purification, Volume 4, Issue 3, September 19090, pp. 141-148; Molecular Sieve Adsorbent Application State of the Art, Anderson, R. A., Molecular Sieves-II, Chapter 53, pp. 637-649, ACS Symposium Series, Vol. 40, 1977; Molecular Sieves for Alcohol Drying, R. E. Trent, a ZEOCHEM undated publication; ZEOCHEM undated Technical Publication entitled Dehydration with Molecular Sieves Fundamentals of Molecular Sieve Design, R. E. Trent Apr. 19, 1992; and Ruthven et al. Pressure Swing Adsorption, V C H Wiley, 1994.
Applicant believes the closest of these references to be WO 2008/089527, which has been published as United States published patent application 2010/0083829, and the R. E. Trent paper and text noted in the preceding sentence. The '527 reference discloses use of pressure swing adsorption with molecular sieves to produce anhydrous alcohol and reveals a number of different arrangements of apparatus to accomplish this result. However, there does not appear to be any recognition in the references of the problem of regenerating the adsorbent molecular sieves other than the conventional approach of using a stream of purified alcohol vapor.
Pressure and vacuum swing adsorption molecular sieves are useful in dehydrating alcohols and other gases or vapors. Molecular sieves used in these processes, on which the water adsorbs out of the gas passing along the molecular sieves, require periodic regeneration in order for the molecular sieves to continue to function.
Known commercial practice for producing dehydrated alcohol uses a portion of the dehydrated alcohol, namely up to forty percent (40%) of it, in a vapor state as a purge gas to periodically regenerate the molecular sieves. The resulting condensate, namely the mixture of the dehydrated alcohol vapor purge gas and water resulting from the regeneration of the molecular sieves, is either discarded as waste or is recycled back into an alcohol distillation column upstream for reprocessing. Such reprocessing is energy-intensive.